That quote is probably the only thing that could qualify as an 'improvement' when FF4 made the transition to America.
One of these days I'm going to write a review of this game...but not right now. Stupid physics test. Anyway, the main thing I want to say is that forced party compositions (which FF4 features) are not a bad thing - FF6, in my opinion, suffered plotwise because it was difficult to guarantee that a certain set of characters would be present. Plus, it encourages the player to pick a small set of characters and go with them. FF4 may have the "final boss is only a plotwise presence in the last dungeon" problem (whereas Kefka is present since the introductory cinematic), but it is otherwise better in terms of plot, characters, and music.
I disagree. FF4 had a couple of tracks that were memorable (e.g. the Calbrena music), but FF6's music was, IMO, the best SNES FF music, far and away (e.g. Terra's theme, the Veldt music, the WoR? airship theme, ...). Bear in mind, however, that it has been ManyYears? since I have played FF4, so said opinion is probably seriously slanted. Plot -- well, I grant that FF4's was more coherent. I just got a little sick of the recurring themes the third time around. Characters... I think it's pretty much a toss-up between the two.
I do concur that some fixed-party sections of a game are good (FinalFantasyNine also has much of the game played with little party flexibility; to be precise, you get about three party choices before the third disc). However, I don't believe that this has to be done for the whole party, all the time. ChronoTrigger succeeds admirably with very little party-forcing; see also SeikenDensetsuThree. While fixed-party elements do force one to utilize the mandatory characters or suffer, allowing some freedom allows for a bit more experimentation with characters who complement the party "core" (or vice versa). (Oddly, though, I'm not wild about the "here's the main character; he'll be in your party the whole game, so you'd better enjoy it") thing.
That said, FF4 does some things well. It has the classical spate of elemental bosses, randomly dropped weapons that are (a) infrequent enough that you won't find all of them in casual play and (b) useful enough to change one's party tactics around when one finds one. There are side quests and fixed optional weapons (e.g. the Masamune). And the game does have a decent difficulty factor.
(but it has indeed been a while since I've played; perhaps I should actually see how badly the FF4 disc runs on a PS2).